The NAND-type flash memory saves data by storing an electric charge in a floating gate of a cell. The electric charge stored in the floating gate of each cell in the NAND-type flash memory is lost as time proceeds, causing a data error. In the present description, a time elapsed until a data error occurs due to the loss of the electric charge is referred to as data retention time.
In order to correct an error due to a lapse of the data retention time, a storage device including the NAND-type flash memory detects an error and performs a refresh control to correct the error (for example, Patent literature 1).